1. Filed of the Invention
The present invention relates to styrene-based polymer moldings and a process for production thereof. More particularly, it is concerned with moldings of styrene-based polymers having mainly a syndiotactic configuration, and having a high crystallinity and excellent heat resistance and gas permeability, and a process for efficiently producing the styrene-based polymer moldings.
2. Description of the Related Arts
Gas permeable films of atactic polystyrene, etc., and polyimide moldings for electric parts having heat resistance (particularly soldering resistance) have heretofore been known. These films or moldings, however, are unsatisfactory for practical use, because they fail to fully meet properties to be required, or they are expensive.
The present inventors' group has succeeded in developing styrene-based polymers of high syndiotacticity (Japanese Patent Application Laid-Open No. 104818/1987). These syndiotactic styrene-based polymers are crystalline polymers and are superior in mechanical strength, heat resistance, chemical resistance and so on to atactic styrene-based polymers and, therefore, are expected to find a variety of applications.
The present inventors' group has proposed stretched films, sheets, yarns, strings, nonwoven fabrics and three dimensional moldings of the above styrene-based polymers having a syndiotactic configuration (Japanese Patent Application Laid-Open Nos. 77905/1988, 259809/1987, 81138/1988, and 98431/1988, and Japanese Patent Application Nos. 3847/1988, 4922/1988, and 161018/1988). Furthermore, it has proposed heat treatment of moldings (Japanese Patent Application No. 3846/1988) and electron ray treatment of moldings (Japanese Patent Application No. 182825/1988) for the purpose of further increasing their heat resistance.
However, in heat treatment, particularly in a case where stretched films are fixed, or stretched fibers are produced, it is difficult to control temperatures at high temperatures, especially in the vicinity of the melting point. In some cases, the films or fibers are partially heated to more than the melting point and there is a danger of break down. Similarly, electron ray treatment has disadvantages of needing an apparatus for irradiation with electron rays and thus increasing production costs, although it is confirmed effective to increase heat resistance.
Stretched atactic polystyrene films conventionally used, when used particularly as vegetable wrapping films, are not sufficiently high in oxygen permeability. Thus a wrapping material having good permeability has been desired. The styrene-based polymers having a syndiotactic configuration as developed by the present inventors' group are unsatisfactory in gas permeability.